The present invention relates generally to cutting tool devices used in milling operations in internal cavities and, more specifically, to apparatuses for providing an internal cavity cutting tool with a stable support that is adapted to operatively engage a cutting device to an internal surface of a workpiece to perform milling operations in a very stable and precise manner within the workpiece.
In the automotive industry the machining and the finishing of precision parts and assemblies have evolved into highly mechanized and highly accurate production processes. This evolution has been driven by the industry""s attempts to create more accurately produced components with closer tolerances. These more accurately produced components are used in vehicle engines and drive train assemblies to increase vehicle fuel efficiency, to provide improved ride characteristics and to increase reliability. Specifically, today""s vehicle drive trains benefit from having more precisely designed and produced transmissions, transfer cases and differentials. To create these components and their various sub-assemblies, automotive manufacturers and component production companies, which supply the manufacturers, rely on precision tooling in various milling, machining and finishing operations to create the required close tolerance surfaces. Not only must the precision tooling must be capable of providing accurate and repeatable fabrication of components in the mass production environment of the automotive industry, but also it must do so cost-effectively and at high rate of speed. The cutting elements of the precision tooling must also be capable of being accurately located against or relative to a workpiece that will become the finished component. This precision tooling often takes the form of various cutting devices that are a part of a multi-function milling machine or a multi-process production system that typically moves the workpieces through several stations, stages or steps, with the workpiece being securely held as the cutting devices are applied to it. Generally, a specialized machine fixture and/or workpiece registration devices control the accuracy of the placement of the workpiece in these machining operations. Also, the cutting device holders which move and/or rotate with the cutting tools have considerable structural strength in an effort to avoid compromising the desired accuracies by deflecting or shifting while performing milling or other cutting operations.
At times it is necessary, in order to machine and finish internal surfaces that will ultimately house or encompass bearings and shaft assemblies, to employ rotating cutting devices inside the workpiece. For example, in the production of carrier cases, which are used in differential assemblies for automotive axle and driveline applications, the cutting tool assemblies are inserted through openings in the carrier case workpiece for the machining of internal bearing and seat surfaces. It has long been known to provide internal cavity cutting tool assemblies that generally have a frame (typically referred to as a hanger), a rotating cutting tool (or body), and a removable interconnection means that provides a rotating drive force from the milling machine""s motor or gearbox to the cutting tool.
To extend the working life of such cutting devices on milling machines, it is known to provide cutting tools with a plurality of indexable inserts for the cutting process. An insert is a hardened cutting bit, generally made of a metal alloy or treated metal, such as carbide steel, that is much harder than the workpiece to be machined. The cutting edges of the inserts are exposed to the metal of the workpiece and are rapidly rotated in a well-known manner in which the exposed cutting edge of the insert shears or shaves off the workpiece material down to the desired shape and dimensions. Making the insert indexable is accomplished by repeating the cutting geometry of the insert""s cutting edge on more than one side or face of the insert. Additionally, the tool body, which holds and locates the inserts, has like recesses, often equilaterally spaced in and around the tool body, that are each formed to accept and retain an insert in a precise placement. In this manner, as the insert wears and dulls along one cutting edge, it can be turned, or indexed, in its locating recess to expose a fresh cutting edge. The indexing of the inserts can often be performed without removing the entire tool body and hanger from the milling machine. This indexing feature greatly increases the useful life of the cutting tool inserts before they must be replaced, which in helps decrease the milling machine""s tool down time and overall operating costs.
The tool body or bodies which retain and precisely locate the cutting inserts are rotatably installed or set into the hanger. The hanger is formed from a generally rigid material, normally bronze. The hanger is normally bored to accept the tool body for rotation. Further, the bore in the hanger and the tool body are arranged so that when the hanger is inserted through a first opening in the workpiece, the cutting inserts in the tool body are generally aligned with the surface or surfaces to be cut. The center of the tool body in turn has a splined open bore so that a splined arbor shaft, attached to the milling machine, may then be inserted through a second opening in the workpiece and through the bore of the tool body. The arbor shaft engages the splines or teeth within the bore of the tool body so that, as the arbor shaft is rotated within the workpiece by the milling machine, the cutting inserts are also turned and applied to the surface to be cut, thereby performing the milling operation.
Forming specialized shapes in the interior portions of a workpiece, such as a spherical seat in a carrier case, are generally known in the art. U.S. Pat. No. 5,232,317 to Peuterbaugh and U.S. Pat. No. 6,220,794 to Calamia et al. are prior type. These cutting devices have rotatable tool bodies with multiple cutting inserts that are designed to be set on hangers. The hangers are moved into an interior portion of a workpiece. They are precisely located by the milling machine and then the arbor is inserted through the hanger and the workpiece, along the central axis of the tool body. The arbor provides the motive force to rotate the tool body, thereby allowing the cutting inserts to sweep an arc having a spherical, or semi-spherical cross-section within the workpiece and cut away material to create a semi-spherical seat. These devices require the use of cutting inserts that are formed so as to have a radial cutting edge. In this manner, as the insert is swept through the area to be machined, the radial cutting edge of the insert forms the radius of the spherical seat.
It is known in the art to use cutting tools to create flat perpendicular seats or seats having a flat surface which is offset from the perpendicular of the central axis. These tools typically use inserts with straight cutting edges and have the inserts oriented within the tool body at the desired angle of the seat to be formed. Quite often, to achieve the desired milling result, the milling process includes using both a rough tool and a finish tool on the same portion of the workpiece in a two-step process. The twostep process is sometimes necessary based on the amount of material to be removed, the hardness of the material of the workpiece and/or desired level of surface finish and/or machining accuracy.
As shown in the Peuterbaugh ""317 patent, the prior art spherical seat cutter 20a depicted in FIG. 1 cuts a spherical seat S on the interior of a workpiece such as a differential carrier case D which is fixedly held. The case D has diametrically aligned bores B around which the seats S are cut, as well as a large opening O at its top. The cutter 20a is supported for rotation about its central axis by a hanger 22a, which is mounted to the milling machine for vertical and horizontal movement. Cutter 20a includes a steel cutter body 26a formed with a reduced diameter section 28a at its rearward end, which is rotatably supported within bore 30a through the hanger 22a. A removable retainer plate 32a is coupled to the rearward end of the reduced diameter section 28a of the cutter body, which retains the cutter against axial movement relative to hanger 22a. An alternative embodiment suggests a double-sided tool body, as in the Calamia et al ""794 patent, which would initially be engaged to cut one seat and be moved laterally on the rotatable drive arbor 34 to cut the opposing seat.
The drive arbor 34 projects through a central passage 36a extending through cutter 20a and is rotatably supported at opposite sides of the differential casing D by stationary bearing assemblies 38a and 40a. The arbor 34a is formed with splines, which slide between and engage complementary splines formed within the central passage 36a. The cutting of the seat in the workpiece D is performed by indexable cutting inserts 42a detachably mounted in the cutter. The inserts 42a include substantially parallel main surfaces 44a intersected by end surfaces 46a to form cutting edges 48a. The inserts 42a are mounted by fastener screws 50a in recesses formed in a front end surface F of the steel body 26a of the cutter 20a such that the main surfaces 44a lie in planes intersecting the front end surface F.
While capable of producing the desired results to some degree of accuracy, these and the other conventional internal cavity cutting tool designs currently in use have their limitations. For example, these conventional designs have difficulty maintaining a high level of accuracy. The hanger tool support member and steel cutter body assemblies mounted thereon of these conventional devices must endure the vibrational shock forces from the cutting of the workpieces and the load bearing of the tool as it is pressed into the cut. These forces, along with the frictional interaction of the steel tool body and the bronze hanger, result in misalignment and cutting inaccuracies to the work surface, especially over time. The tool support members are also susceptible to certain amounts of lateral deflection or distortion, which adds to inaccuracies in the work surface.
Additionally, the conventional devices also rely on the splined arbor to provide alignment of the tool body to the workpiece. However, spline drivers are, by nature, rather sloppy and do not work well as a precision locating device. Since they must slidingly engage and re-engage, splines are typically loose tolerance devices, and are generally only suitable for accuracies on the order of 5 thousandths of an inch. Thus, by supporting the internal cutting tool through the insertion of the splined arbor, these conventional internal cutting tools all have problems with rapid tool wear, tool chatter and mis-positioning.
Finally, conventional spline assemblies have spline teeth that are cut in a generally square manner. This, in conjunction with a free turning tool body, typically requires a human intervention to align the splines of the arbor and the tool body correctly as the tool is inserted in the workpiece. In some cases, the conventional cutting tool devices have a solenoid operated tool body brake or stop which holds the tool body in place once the spline arbor is withdrawn. In this manner, reengagement can be performed automatically, that is, without the machine operator having to physically align the spline teeth. This is of benefit for repetitive arbor engagements. However, this still requires initial operator alignment and such a tool body brake adds substantially to the complexity and cost of the tool.
Thus, there is a need for an internal cavity cutting tool assembly which overcomes the foregoing limitations of these conventional designs. In particular, there is a need for a cutting tool assembly that eliminates or at least dramatically reduces the inherent machining inaccuracies of the conventional designs using a splined arbor and conventional tool support. Also, it is desirable to extend the useful life of cutting tool inserts in order to lower production costs and reduce down time while reducing tool chatter and improving milling accuracies.
The present invention overcomes the disadvantages and drawbacks in the related art as an internal cavity cutting tool, which includes a rigid tool hanger assembly providing precision locating of the cutting tool within the workpiece. The present invention provides an internal cavity cutting tool assembly including a tool hanger assembly with a tool hanger body, a bearing assembly, and a bearing retainer plate. The tool hanger body is defined by a general xe2x80x9cLxe2x80x9d shape having an elongated leg and a long and further defined by a first surface and a second surface along the elongated leg. The elongated leg further has a through-bore disposed through a first and second surface, the through-bore further having a bearing seat that is adapted to receive the bearing assembly. The tool hanger body is adapted to receive the bearing retainer plate, thereby retaining the bearing assembly within the through-bore of tool hanger body.
Also included is a tool body assembly having a first or upper tool body portion and a second lower tool body portion. Each of the tool body portions have a splined arbor bore, a cutting face having a plurality of insert pockets, a plurality of cutting inserts, and a stepped radial portion defined by a bearing support surface. The bearing support surface of the first tool body portion is adapted to be received by the end of the through-bore in the first surface of the tool hanger body and the bearing support surface of the second tool body portion is adapted to be received by end of the through-bore in the second surface of tool hanger body, such that the bearing support surfaces of the tool body portions oppose each other within the through-bore of the tool hanger body, each of the plurality of insert pockets disposed within the tool body portions is adapted to receive one of the plurality of cutting inserts.
A splined arbor drive assembly having a splined arbor drive shaft and an arbor support is also included. The splined arbor drive shaft is operatively inserted though openings in a workpiece and through the splined arbor bore of the tool body portions into the arbor support. The splined arbor drive shaft and the arbor support are adapted to be retained in a milling device to operatively rotate the splined arbor drive assembly and the tool body assembly while precisely locating the tool hanger assembly, thereby sweeping the cutting inserts disposed in the tool body portions against the portions of the workpiece to be cut.